Scientists have recently purified androgen binding protein (ABP) and prepared an antisera to it. We are attempting to localize ABP in testis and epididymis using immunohistochemical techniques. Our preliminary results indicate that ABP is present in the cytoplasm of Sertoli cells, as expected. Little is known about the function of ABP in male reproduction. We hope that by determining precisely where in the male reproductive tract it is present, we may learn more about its role. Germ cells migrate from the base of the seminiferous epithelium to the tubule lumen, presumably assisted by active movements of the Sertoli cells. The Sertoli cells also engineer the release of the late spermatids into the tubule lumen. We have obtatined antisera to actin and myosin and are attempting to localize these stuctural proteins in the seminiferous epithelium. We hope to learn more about the molecular mechanisms by which the Sertoli cells cause germ cell migration. We have well fixed testis from monkeys and humans. We are continuing our fine structural examination of the primate testis.